Do you think this is justified? Lawmaker uses Canadian case to criticize Obama

Short answer to your question is METT-TC (it depends). The long answer is best boiled down to a few bullet points:
- Americans should be able to disagree internally but we used to do a far better job of presenting a united front outside the US. We have gotten progressively worse at this to the detriment of our national interest.
- Arguments should be able to start with facts, follow a logical sequence, and conclude with a reasoned recommendation. Think 15-6 and facts, findings, recommendations. This level of logic is generally missing in today's political discussions and media coverage. Facts are generally cherry picked to support pre determined positions rather than allowing a comprehensive review of the facts to drive findings and recommendations. Again this is to the long term detriment of US strategic interests.
- Comparing and contrasting can be illuminating. In this case, the Canadian PM's immediate classification of this event as a terrorist attack vs the Obama Administration's response to this event and its classification of the 5 NOV 09 Fort Hood Shooting as "workplace violence" is illuminating in my opinion. How can we effectively combat radical Islamists if we are relucant to even use the words?
- To specifically answer your question, not every foreign incident should be used to take a swipe at POTUS for whatever reason but some incidents can and should in order to highlight problems, issues, or risks posed by whatever the administration is or is not doing.