Grandkhan is right in the description of the landcruiser. This is the real life design they are modeled upon:
http://en.wikipedia.org/wiki/Landkreuzer_P._1000_Ratte
I fully agree with Grandkhan, in most/all circumstances such a vehicle is thoroughly impractical, especially if your enemy has any sort of bombers that they could use against it. Scandinavia did not have any sort of bombers they could use against it. As for the earth, yeah, such a beast would tear up even paved roads and in boggy terrain would likely sink and have severe difficulty, if incorrectly maneuvered. The Russian landcruiser was designed for a single purpose: creating a vehicle that could breach the Mannerheim Line, and perhaps wage defensive fights against German armor on open steppes. A mobile battle against superior firepower? Very much no. For either of these purposes, the landcruiser is ideal. So far, these vehicles have not proceeded beyond the original use of breaching the front line.
EDIT: Symphony made the point quite well. I lived in the KSC area for a while, and yeah, it's pretty darn marshy and wet.
Crezth made a comment about how he was disappointed that the Scandinavians could not build a defensive line that could stand up to artillery, and Shadowbound (correctly) pointed out that the Maginot Line actually did quite well against direct German assaults. To address the first, a landcruiser is not an indirect artillery piece, like the infamous rail gun the Germans used OTL. It is meant for direct fire capacity, with the option of indirect if no other option is available. Having actually spoken to people who spent time under fire of both in the Second World War, I can assure you that direct fire is a completely different beast than indirect, and far more devastating to the target. Because no RL installation ever faced direct fire from twin 240mm cannons, we can only hypothesize as to the resulting destructive effect. The armor of the said vehicle is more than sufficient to responding to the guns that would be present for direct fire on the front. The biggest threat to the landcruiser, close air support and heavy bombers, doesn't exist. The Scandinavians have had no such aircraft. Combined with actual rail-mounted heavy artillery like
Dora present (three of them in fact), we are talking about a devastating attack and firepower that the Scandinavians could not effectively respond to. Of course this is incidental, the Russians also attacked with nearly 10x as many soldiers as the Scandinavians could effectively field on the battlefield. The outcome was unlikely to change, the presence of the landcruiser and heavy cannon only helped reduce Russian casualties, and perhaps shortened the battle. As LoE pointed out, holding the Mannerheim Line was never the plan, but I hesitated to mention that before he did because, I figured that I should not be the one to actually reveal what players have planned, even in the update.
In terms of Russian numbers, I must disagree with Shadowbound that they are at a ridiculous level, and based on my research of primary sources from the OTL time frame, as well as modern agricultural production and statistics, which I looked over last time that was brought up, I believe the current situation IS plausible. At the same time I will acknowledge that as the best sources available directly from the time frame are written by the Soviets, it's highly unlikely they are accurate. I can only work with what information actually exists and is not written in Russian. All evidence points to the Russian army size and mobilization being theoretically possible, under the correct circumstances.
In strictly numerical terms, Russian victory is not inevitable, even if the situations in Germany and Scandinavia are as dire as they may appear. Heh, just wait until you see the casualty lists.