The game isn't at that low a resolution. The on map units are regiments or larger and they pay extra movement points to cross rivers.
Scale isn't much of an issue when it comes to bridging units, as there were no true dedicated bridging units as regiments. Most units were company size or possibly battalion size and could build boat bridges, the units were not intended to build permanent bridges.
Of course, the Germans did not have Bailey bridges and the larger Bailey bridges covered about 350 meters and would be incapable of covering many of the major rivers in Russia without supporting pillars in the actual river, which would be fairly impossible in the Strait of Kerch unless they were on barges.
Although it would, of course, be possible to build a bridge across the Strait of Kerch it would be more than a few engineer units could handle in a limited amount of time. Most divisions lacked the equipment to cross such an obstacle within a practical timeframe (a day or two) in general without help from boats or barges.
I understand that the designers can't make every river unique, as that would be very impractical, but being able to cross major rivers with units that didn't have the equipment to do so would be quite gamey.
Can actual bridges be constructed on the map as permanent features, or are they tied to an engineer unit with pontoons remaining at the location like in, say, the Decisive Battles series?
The actual mechanics of how Axis Allies surrender or defect have yet to be determined. Currently Slovakian divisions have a fixed withdrawal date but that may change if a mechanism can be devised that won't be subject to player abuse. Sorry but I cannot be more specific than that at this time.
OK. Earlier on, you made it sound like the mechanics of Slovakian surrender were fixed and would not be altered, whilst the surrender mechanics of the other minor Axis nations were still being worked out, hence my surprise.
I'll save further questions on the matter until the game is closer to release.