Idle thoughts as the Vilnius Union contemplates having Mayan neighbours up against the Canal Zone.

1)  If the Mayans deployed 27 land and 4 air units against Costa Rica, they would almost certainly deploy as much or more against the Canal Zone if there was a Panamanian Boogaloo.  The Union doesn't have anything like that kind of power in the region, and doesn't have the extra deployment points necessary to allow a quick build-up, either.  So that's a problem.

2)  The Union has very little strategic depth to the west of the Canal.

3)  The Union's ability to reinforce from overseas is predicated on at least temporary control of the seas. 

4)  It does benefit from having multiple ports in the area, which will be most useful if there are significant roads and railways between them and the canal zone.

5)  It theoretically has a tech advantage that may be offset to a point by the limited number of land techs that the Mayans need in order to be competitive there.

6)  The terrain and weather isn't always going to be favorable for combat so that will need to be understood.

7)  There will be an increased interest in naval forces capable of supporting a land campaign along the Isthmus, though that's more the navy's problem than the army's.

1A. The last 'Colony Count', the HY1 1923 one credits Wilno with 23 excess deployment points, and capable of an offensive amphibious lift of 31, so 8 short of actually using the [full] amphibious forces.

1B. Per the rules, forces deployed to a territory for a while gain some bonuses. Currently that is the 'dug in' which really helped. While more than the rule version, it certainly 'feels' like the right level of defensive bonus.   

1C. Defenses LP/AP deployments are different than Offensive.  For Offensive, you need the DP, which form the  organic support elements and live/die with their AP/DP. Defensively, You can support forces in-Region equal to the IC in that region without needing deployment points. LP/AP in excess of those IC do need deployment points.
This makes large regions somewhat more resilient.

2. Yes, the strategic depth that you had was lost. You still have a larger overall region with strategic ports. One redeeming factor is - if the Mayans continue to hold the 3 provinces - the will not be 'Homeland' and the Mayans will need DP for LP/AP there.

3. SLOC are intended to be important.   The cases where there is a Homeland adjacent are where things get a big problematic.

4. The supply system I wrote up pre-war has not been put into place as it would have crippled the Japanese for lack of a major port. Rather I am using a mixture of WWII logistics data, and notions from military history.  In the future there may be a more defined supply system, but ports and provinces with IC will factor in. It is critical to remember that history was changed here, so the Americas were not depopulated and large areas are still agricultural. Further, non-IC areas are more at the 'baseline' level, which is ~US Civil War or British India - there are many minor roads and low-end infrastructure, just not much excess production.

5.  The Mayans are 7 years behind the date, with 2 advanced categories. I also opened a can of potential worms by allowing the 'purchase' of Air Points. That happened to fit what the last Iberian player wanted. Only a handful and added a little surprise. My intent there is the Advanced Air Points are a Non-Upgradable purchase, so if the Mayans wanted 1922...they'd have to buy them all over again.

6. Heavy Weather matters strongly for Air and Naval Operations, as they are done on a weekly move.  The Land forces not so much as that is more a monthly average, though I would take it into account if I rolled several storms.  Strategically it can impact supply lines.

7. Well that's part of the lovely strategic puzzle.

Observation :
The Mayans were brusque neighbors, but for several years had overwhelming force adjacent to Wilno and did not invade.
Indeed, they have characterized this war as the continuation of a prior conflict.
Currently, they likely have sufficient force to continue into Wilno territory, but have made efforts not to inadvertently do so.
The Mayans have indicted unhappiness with Wilno, and made some clear statements on that matter, but have not actually threatened to invade...