There's a form from CBSA for Canadians to bring airsoft out and back into country but I'm not sure how it will work for Americans. Best course of action is probably to rent up here and slap on your accessories onto the rental.
Also check up on ITAR restrictions, it's not a CBSA thing, it's a US Border Services thing where they don't want weapons tech to get exported and leaked outside of the US.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE