I actually just re-located back to Canada from the US. When we moved there I brought all of my firearms with me. The biggest pain was getting all of the paperwork processed through the ATF so I could import them into US. If you plan on going this route, plan ahead as it takes a while to receive paperwork back from them. If you reload you will need to account for those items as well.
Biggest pain I found is when I returned to Canada for hunting trips I had to stop at the border crossing to complete temporary export paperwork (there is another name for it but can't recall) so that when I returned I could bring firearm back without hassle. It doesn't sound like much but it takes a fair bit of time, and border crossings can sometimes be rather busy.
When we moved back, it was quite easy as I had kept my PAL current. No questions at all when we crossed.
As for markings on the firearms as mentioned before, I never had to go through any of that, but of course your experience may vary as I am a dual citizen.
If you know your stay is going to be temporary, I would just leave them behind if you have the option and buy something down there. Never a bad day when you "have" to buy a new gun
