Here is the bottom line.
Styrak your actually wrong. Getting your guns back and forth is very plausible and pretty easy. I have been doing it for a little over a year now.
LanePratt summed it up ok but I will add to what he has done.
First and foremost, a Y38 is nothing more than proof the item was purchased in Canada, but does nothing for admissibility based on velocity.
Basically, if you have a Y38 and gun does not meet the velocity outline of 407 FPS and its not CANSOFT than your gun can be taken for testing or seized.
The additional document you need is a form from an "Expert" that states that your gun meets the additional requirement of shooting 407FPS but bellow 500 FPS.
I had my local registered Gun Smith classified an expert by the CBSA and he has been certifying my local guys for OPP at Fort Drum.
I have heard of guys getting by with just a Y38, but there is still a high risk of "black" guns getting seized.