well i still say first we know film will be all ww2 so no worries there. As for how he is getting frozen or what not there is a variety of ways they can go into it. A, to the classic move he is trying to stop a bomb from going off its flying over a frozen tundra spot/The artic and he stops the bomb but is flung into the cold water or into a frozen mountain side. B. Maybe they can go into saying Red skull was working on some cold fusion bomb or early suspended animation stuff. So say if its a bomb it goes off with rogers riding it lets say and its over some barrien cold place like option A but its not the cold that freezes him its the fusion bomb that froze his cells and he is only kept alive barely due to the SSS. OR you can say if its suspended animation thing maybe red skull had a base it was at in the artic tundra like i said red skull and steve have a showdown there the allies nuke the place but both rogers and skull are in a underground chamber were the equipment is the bomb knocks out the base and triggers some instant freezing and both are frozen together. Or steve due to SSS isnt frozen as soon as skull is and gets a bit away from him and is frozen. To be found in the present day. Then you can say since steve wasnt in the same spot as skull maybe an assoicate of skull found him in suspended animation after the bombing. They take skull's body with them. And dont notice steve's body maybe cause with the blast that took out the base maybe he was under some frozen rubble or what not. Then like i said we know the film will have to lead into avengers. I think it would be nice to have that after credit scene(and internet savy folks would know of it to stay and watch) and then after the showdown with skull and rogers it flashs to present day. Shield is working with X government at the site of the base which was found and roger's suspended animated body is found for option B. and for option A like i said before if he was frozen in ocean or a mountain side to maybe go some divers/hikers find something. This leads to Shield going to site. Then we end scene with X shield members(fury and/or stark) finding the body. Then the last moment we see steve in hospital setting and he awaken. Then The avengers film can pick up right at that moment. Or they can say maybe a few weeks or months happened between rogers waking up at the closer of cap film and avengers film.