Actually, it's far more likely to come via Canada. The Millenium Bomber was just one example.
Muslim terrorists are much more likely to speak English than Spanish.
Muslims find it much easier to legally enter Canada than Mexico.
There are numerous communities to serve as support groups for Muslim terrorists in Canada, virtually none in Mexico.
It is easier to cross the Canada-U.S. border undetected than it is to cross the U.S.-Mexico border. There are miles of unfenced open spaces between the Prairie Provinces and North Dakota and Montana.
If I were planning to infiltrate Muslim terrorists into the U.S., I'd do it via Canada.
Not really. Mexico has a very large Muslim community and it's just as easy for them to get a visa for Mexico then it is from Canada.
Middle Eastern males can blend more easily into a group of Latin Americans then they can a group of Caucasian Canadians.
Far more illegals from the Middle East are apprehended along our southern border then our northern border.
You made several good points about Canada being a likely point of entry for terrrorists.
I would like to make a few points about the possibility of Mexico as a point of entry.
At first glance, many middle easterners have similiar skin tones/hair color to hispanics. That fact might lead them to believe they can "blend in" better on the southern border.
Many more illegal entries are made on the southern border, stretching the capabilities of all available enforcement agencies so thin the capture of terrorists would be less likely.
Human smuggling is more highly developed and organized on the southern border, so it would be easier for them to pay someone to smuggle them in. The human smuggling network on the Mexican border has links to every major city in the US.
Though I believe you are correct that support groups are more available to Muslim terrorists on the Northern border, corruption is so widespread in Mexico, even at the official level, support could easily be bought in Mexico and in border areas on the US side.
I admit I have never been to the Canadian border- but have you seen the remote areas of the Mexican border? There are many, many miles of remote areas of the Mexican border with little to no fence or markings. As far as ease of crossing the actual border; the millions of illegals that have already crossed are pretty good proof that it isn't hard to illegally cross the Mexican border.
If I were a terrorist, I would come in through the Mexican border, where crime and illegal entry are much more common, in all the chaos on the southern border I think I would be more likely to pass through unnoticed, and would bet I would be able to buy my way out of trouble if something went wrong.