Originally Posted by GalinHdz
Since there is no ADIZ between the US and Canada, 12" Numbers are not required.
True. However he may be concerned with someone at the border flagging his 3" numbers which don't meet Canadian regulations. But that doesn't matter as he's flying a foreign-registered aircraft.
I used letters purchased at Staples to mark my RV-6 when I imported it from Idaho. The previous owner had used similar letters, so it was a simple matter to peel them off (15 years old and they came off without issue with a little thermal persuasion from a hair dryer).
After importing, I had new letters made to my specs and stuck them on. 10 years later and lots of polishing over top of them and they're still sticking fine.