Just so I understand this correctly:
The PMO ought to be free to decide on a whim who enters and who doesn't?
In a democracy, I don't think so. We decide collectively, directly through voting, and indirectly through our representatives enacting legislation defining who can enter and who cannot. In that way, we decide collectively as a democratic people who can come in ad who cannot. Whether Galloway can enter Canada or not should not be at the whim of the PMO, but rather in accordance to established legislation parliament has agreed to.
No you say Galloway has indeed violated Canadian laws. Fair enough. But if he's violated the law, then the right thing to do is not to tell him he can't come into the country, but rather to warn him that he have a warrant out for his arrest, even requesting that he come.
Also, if indeed he has violated a Canadian law, seeing that the UK is supposedly an ally, we should formally request extradition.
Either he's a criminal or he isn't. We can't have it both ways. If he's not a criminal, then as long as he meets whatever established requirement to enter the country, we should let him in. If he is a criminal, then we ought to prosecute. Which shall it be? Or are some foreign nationals more equal than others in Canadian law? If that's the case, then let's legislate accordingly, making it clear that foreign government representatives are granted diplomatic immunity from Canada's counter-terrorism laws. Of course if that's the case, why was Saddam Hussain not exempt?
No matter how we cut it, we need to follow through with the same standard for all. Our refusal to grant him entry is suspicious at best.