1. Depends on what it's made of. Non-assembled sesin parts can be imported, airsoft without an importation license, no. I had to Han Solo mine in (years before I became a Customs Officer). I ordered a resin Shorty Spulse and it came in no problem. Licensed airsoft dealers can import them, and ultimately... they'll be expensive. I have seen an airsoft PR for sale Toronto Airsoft.
http://www.torontoairsoft.com/Snow-Wolf-Alien-M41A-Pulse-Rifle_p_2233.html2. Suppliers can ship all they like, but if the receiver isn't a license airsoft merchant, this is where it'll get seized. The importation of airsoft without proper licensing is prohibited. So basically, not in the passenger stream, only the commercial stream.
3. There are no local Canadian merchants of resin Pulse Rifles that I know of.
4. I see hunting rifles and handguns come in all the time here, but the issue is that these are licensed firearms with valid ownership and brought in by either a resident of Canada with a Possession and Acquisition License or a foreigner properly declaring and paying for a temporary importation license. The problem with airsoft and an assembled resin is that it falls under a replica category which is prohibited in Canada. So, again, you need to be a licensed commercial importer. I would not risk temporarily exporting my PR out of Canada for fear of losing it (and my job) upon return.
Hope this answers your questions.