Importing restricted items is ILLEGAL. Whether the final product is used on the field or hung on your wall in your den makes no difference. The act of importing it is what is illegal. Simple as that. You got lucky and managed to get something across the border by mail. Lucky you. For any restricted item (full gun, AEG receivers, pistol frames), you can expect to pay 2-3x what you'd see out of country. That's the price of airsoft in Canada, whether we like it or not.
And quite honestly, by having publicly announced that you wanted to get 500+ fps AEGs to shoot cats in your back yard, you've pretty much guaranteed that any age verifier will always be "too busy" or "out of town" and won't be able to meet and verify you.
What I would strongly recommend is that you spend more time reading these forums and seeing how the community operates, and less time starting new threads and repeatedly shooting yourself in the foot.