1. The holder can back forth
U.S./Canada without any problems. He doesn't need a visa to Canada, nor a visa back to U.S. It's alreay multi-entry on both sides. (But cannot stay in Canada over 30 days)
2. He can apply multi-entry H-1 visa stamp in Canada, but if refused, he cannot come back U.S. So why apply something already has and risk himself?