is there a way to perfectly mix air sea land combat together

Soo most maps either have
Land and air combat
Or land and sea combat
There are rarily any MAPS that mix all three
And the ones that do usually have it forced in like maybe having a small sea area
Or having airports not being accessible from the start opinions please

It's not really possible, no. The main reason for this is that sea combat in Advance Wars is not at all balanced with the rest; all sea units are ludicrously overpriced. Therefore, in a battle with land, air, and sea, the air and land will always take precedence in optimal play.

Yeah naval is pricey but on quite a few maps you have little choice but to go to sea.
I think it is just a little unexplored as yet.  Because already with land we have a potentially rich environment with many possible geographic arrangements with mountain rivers forest and many possible kinds of arrangement of properties too.  I think its just the community is still quite young at ten years old and hasn't got to that point yet of big "all media "battles being commonplace.  
However there are some maps where there is some mixing of land air and sea units in battle. We can search out some and post here for interest.
This kind of topic had some discussion in the old forum from time to time. (Linked from awbw playsite in read only status)

As Morgan said, expensive naval units make it very difficult to balance land, air, and naval.

Balancing air and navy on a map that has little in the way of land fronts would probably is easier by making there be drawbacks to relying too heavily on cheaper air units. It could be anything as simple as airport positions or designing the map to benefit naval units more, to more creative solutions like pipe blockades or predeployed missiles/carriers etc. Unit bans can also help with that; setting b/t-copters as bans or lab units obtained later in the game could help naval battle develop a little more easily.

When you introduce land into the mix, the viability of naval units decreases substantially because of what you get out of it. Think about it: Do you want to spend 28k to have a unit just so you can assist in land combat close to shore? Or 18k to protect your 28k from copters? Why would you do that when you can spend 15k on a rocket or 8/9k on an AA or bcopter to deal with copters? Even a missiles for 12k is cheaper. I think it would be very difficult to find a near-perfect balance simply because of how much cheaper and more versatile air units are.

If it weren't for the fact that naval units were so specialized and expensive, it wouldn't be an issue. Land units are cheap and specialize in the most common form of combat in the game. Air units are more expensive but can attack just about any unit in the game and cross over just about every terrain in the game. Naval units are even more expensive but instead of gaining more abilities, they lose the ability to attack many units that air units can (on a per-unit basis), can only travel over water (not even rivers or shoals*), and are highly specialized for a portion of the game that inherently has less value (they can't capture properties, take advantage of land-based meatshields, etc.).

*Transports don't count for naval battle

I want to say more and read this over a bit first, but I'm in a rush so I won't. I just wanted to throw another opinion into the mix.

Its possible to get great land sea air battles IMO.
Pacific Bay gives plenty of land sea with some air .  

http://awbw.amarriner.com/prevmaps.php?maps_id=5187

A slightly more central airport would get nearly plenty of all 3 forces.
Some maps simply require all 3 forces.
This would be interesting map category. Such games get very interesting and usually very imbalanced and fluid due to much larger number of strategy choices available.  If anyone has more good interesting examples of land sea air maps please post here for perusal.  I guess many of the awbw site "heavy naval category " also have air.

Edit.. Though yes with my example the naval gets heavy because of the slowness and farness of airport.

Just set Limited High Funds on a sea, land, air map. Solves all your problems right there.