DORADO
The areas surrounding the 3 checkpoints of Dorado all contain important highgrounds that give an advantage to whoever can 'control it better' - defenders will automatically take control of it first but this doesn't mean they can always maintain it. Attackers can penetrate the highground rather easily as Dorado leaves a few different openings to get to the highground, but to aid in this pursuit I'd recommend playing long range, mobile heroes. For example; Winston, Genji, Tracer, Ashe, Kiriko, Lucio. Snipers like Widow, Hanzo and Ana work especially well on these types of maps as it consists of long sight lines and an array of highgrounds. Dorado can feel relatively cramped in some areas on the low-ground and as an Ana player who usually has to push payload on attack, and therefore play in these areas, I would recommend pre-planning what you would do in certain situations - this can save you from panicking and knowing where to go if in danger.
HAVANA
Havana is an excellent map for long range heroes - especially snipers - They will most likely win fights over short range heroes like Reaper or Brigitte due to the long sight lines. Although there is a fair bit of coverage on both the attack and defense the most crucial highgrounds being in the first and last checkpoint can win or lose you games. The best tanks to play on Havana are most likely to be Sigma because of his moving shield or Winston as he can easily dive snipers. For other roles, again, snipers are a strong pick - Widowmaker, Hanzo, Ashe (with a Mercy pocket). Mercy's damage boost on this map is very strong as you want to avoid damage drop off as much as possible. Supports like Ana, Mercy, Kiriko, Zen are very good for this map because they either have mobility or range. Flanking is not crucial but is easier due to the different points of access around the map and can make winning team fights smoother. Lastly, Widowmaker is mostly always picked on this map at some point or another so always make sure to double check before peaking!
JUNKERTOWN
Junkertown is an odd mix - the first checkpoint is incredibly good for sniper heroes but this can get harder going onto the second and third checkpoints. On the latter half anything from Rein, Winston, Sigma, Symmetra, Junkrat, Ashe, Reaper, Ana, Mercy to Brig can work as the sightlines get more narrow and it's easier to deal damage with an AOE hero or short range heroes in more enclosed spaces. This obviously does depend on how each team is playing and counter picking certain heroes can be your best bet at winning. For each checkpoint, though, you wont go wrong with picking a hero with an ultimate that creates a lot of space - D.Va bomb, Rip-tire or Gravitic Flux as the space to move around the payload lessens with each point. Try have an awareness for what your team needs or what the enemy team will struggle against as Junkertown can be completely situational.
CIRCUIT ROYAL
Circuit royal has mostly medium sightlines except for at the beginning and the end points. Heroes that usually do well on this map are long-ranged or snipers. This map is amazing for Sigma to which he is probably the most played hero. Widowmaker would probably be the second most played. Other heroes that I see a lot of too are Winston, Echo, Hanzo, Cassidy, Ana, Kiriko. The maps overall natural cover is ok but I wouldn't rely solely on it; having a tank that can provide cover is extremely useful as the highgrounds are quite domineering but relatively easy to fight for control over. The biggest problem on this map aside from the highground is how narrow it can feel - Try to pre-plan to avoid getting caught out by the enemy team whether this be on offense or defense.
RIALTO
Widowmaker is a powerful pick on Rialto due to the long sightlines on the first and second points. Any form of sniper is good on this map though and can be more tricky to defeat, you will most likely succeed playing long range heroes too not just snipers. Taking control of highground can really benefit your side as it gives an automatic advantage over the enemy team. This does change on the last point though as the sightlines get extremely narrow and objects including the payload can obstruct your view very easily - flanking heroes like Tracer or Cassidy can be strong picks, whether it attack or defense, alongside a strong frontline such as Reinhardt or Sigma with a Zen and Ana. These are just rough suggestions though and you may benefit going a hero that can zone areas or a hero that counters another.
ROUTE 66
Route 66 has it's fair share of high-grounds that are especially effective as mostly every point has one that oversees the payload. Heroes such as Baptiste, Pharah, D.Va, Ana, Ashe are just a few examples of useful heroes due to how this map is structured. Route 66 does have a weird shape to it that features a lot of bends and curves which can make heroes with abilities that can clear or deny areas very strong (Mei wall or Hanzo Dragonstrike). Even though it has a lot of bends it does have quite long sight lines with a lot of open space - this can make squishy heroes very vulnerable. Playing around healthpacks can also be very strong as there are several crucial large health packs on parts of the map - Your team could benefit from a sombra in this instance or mobile heroes that can reach these packs. Mobile heroes in general are great for this map though as you will need to fight for those very important high-grounds.
SHAMBALI MONASTERY
Shambali Monastery is one of the newest maps in Overwatch 2. Highgrounds on this map are, again, quite important to maintain especially since on the first and last points they overlook the payload. I personally believe that brawl is a good way to go about this map so Reinhardt, Ramattra, Cassidy, Soldier, Ana, Lucio just for example - mid to long range heroes are good for this map even some short ranged heroes like Brigitte can be played well. Flanking and getting picks is easy on this map because of the many pathways around each of the points and healthpacks. Rely on cover on this map since there can be weird angles and open space that can put you into immediate danger.
WATCHPOINT: GIBRALTAR
Gibraltar has a lot of eleveated vantage points with it having the most high-grounds in the game. Characters that can close these gaps will win you the match as the distance from the low to high ground is quite extreme and similarly to any other map whoever can control it better will win. I recommend playing snipers and mobile heroes - Winston, D.Va, Tracer, Genji, Ana, Mercy Widowmaker, even Pharah - these are all strong picks that can change positions fast. There is a lot of open space on this map so heroes that require more enclosed areas to deal damage (Mei, Junkrat, Reinhardt) will struggle a lot more and most likely rendered useless by longer ranged heroes. I really suggest planning your pathing on this map, similarly to Dorado, because you may find that angles can be awkward or tight and although there is means to escape you can panic and die very easily if you have the enemy drop down or jump up into your face. Use the array of health packs and backrooms to flank and force enemies out of position.