Hi Just checked with CFP at 1800 731 4000 and yes it is legal to import air pistols from the states as they do not look like a replica firearm and they are same model they sell up in canada and less than 500 fps. There may be duty but CFP states it is a non firearm so it is no different than any other goods you bring up from the states. They will not be seized at the border like you stated and, like my original email states less than 500fps
It is nice to know if your shopping in the states (150 km's from home). D&L is 3000km's or miles away. If your not sure if the model you want to bring up is legal give CFP a quick call they were friendly and very help full.