1. It's not a racial issue, it's an economics issue. The Economy of Canada is doing fine, and the standard of living in Canada is comparable the US, Canadians don't really tend to cross the border to come live in the US illegally, and technically, they can legally apply for jobs in the US and get a permit to come live and work in the US once they have the job. Unlike Mexicans and Central Americans who's economy and standard of living is way below the US poverty standards and require hardline visas to enter.
2. True, but again, Canadians don't cross illegally to live in the US because their standard of living allows them to live properously in their own country. For persons of poorer countries, getting into Canada isn't a way to sneak into the US at all. If Canada bordered Mexico, they would have the immigrant problems as well, so it does not work the same way!
3. It is very difficult to enter Canada and then cross the US border illegally via Canada. While I can't say people haven't tried, if someone gets permission to enter Canada, their comparable standard of living is good enough that they would not need to cross the border. It's probably an idea people have, but it's not really feasible. You don't really see the a large number of non-Canadians entering the US illegally through Canada, and you never see Canadians doing it at all. Canadians cross over every day at their disgretion for temporary stays. It is NOWHERE even FEASIBLY close to the problem of 8,000 Mexicans and Central Americans cross the border BETWEEN THE US AND ARIZONA only, per day. You may have 1 or 2 crossing illegally from Manitoba to North Dakota per month.
4. Security of What? Canadians and Americans work together in terms of securing their large border, hence why it is undefended. There is practically NO problem when it comes to Canadians and Americans crossing the borders as some people actually own land that is on both sides of the national border. I'm sure you don't mean Canadians are actually crossing over into the US illegally, they wouldn't need to, while if you mean non-Canadians, that in itself is a near impossibility already and probably happens too little to even be enough to think of building anything on that border.
Like I said, it's an economic issue, and the economy of Canada is in great shape.