No where does Harper mention clear support for a North American Union. He may have toyed with the idea, but never seriously, or at least not now. If he did consider it seriously, it would be a major debating point today. As for the SPP, that's strictly a military and economic alliance, not a total union.
Now I'm for world federation, but with so many conditions that even I would not likely jump into any union too quickly.
As for Harper, who knows. Maybe he does support such a union in principle, but it doesn't seem to be a priority for him any time in the near future. So I don't think that's a major issue right now. And with the US economy now, Harper is even less likely to want such a union any time in the near future until the uS cleans up its economy, and that's IF he even agrees with a union in principle, which you have yet to prove more conclusively.
Doea Harper have it in writing? I say alot of things in speech that are only considerations, not commitments. Even if Harper should have mentioned support for such a thing, unless it's in an official policy statement in writing, it may just be that he was contemplating the idea, not committing to it.