The Canadian Communion blunder
Canon 844 specifies the conditions under which a Catholic minister may licitly administer Communion to baptized non-Catholics and none of its five sections, including the most relevant section 4, seem satisfied in this case. I see, for example, no "grave necessity" for Harper to have taken holy Communion in the first place, it is doubtful that he approached on his own accord, and there is no evidence whatsoever that Harper "manifest[ed] Catholic faith in respect to [this] sacrament". Any one of these points, not to mention others, stand in the way of Harper licitly receiving the Eucharist.
For this grave blunder, however, I do not tend to hold Harper responsible, though he might have been poorly advised by his protocol staff. Rather, I look to the archbishop who, as the chief presider over the Eucharist in his local Church (1983 CIC 389) and as the one charged with upholding ecclesiastical laws and sacramental discipline (1983 CIC 392), should have known better.
In any case, I hope his Excellency's office is vigorously pursuing the question as to what happened to the Body, Blood, Soul, and Divinity of Our Lord last seen headed toward a politician's pocket.
Update: Sources say Harper consumed the Host, some claiming right away, others, just after Mass when he asked a Catholic what to do with it. Either way, the PM's decorum is commendable. Now, about Catholics putting Protestants in such positions to begin with . . .