I guess it depends on how you view it? I do realize that Canada has safety standards for all seats, however, it is my understanding that these standards aren't necessarily the same as what the manufacturer will actually test for. For example - side impact. It isn't required to test for this, but a company that DOES will impress me greater then one that doesn't. Another example - anti-submarining clip on boosters. These makes sense to me. No, they aren't required, but it seems like Britax going the extra mile. Also, recall policies. Different companies, different policies. A company that is reluctant to recall a seat does not earn my confidance. I also find the frame and fit to be a factor. Sure, the seat passed the safety standards, but if it doesn't fit my tiny kiddo well, then it's not as safe as another seat. I am most certainly not after a "cute" cover.
For a company to receive the National Safety Mark, the maple leaf sticker that goes on the seat, they have to meet the stringent testing that Transport Canada has put into play. If they do not meet it, the seat cannot be legally sold in Canada. The testing is very specific and very good. It also provides a baseline that all seats must meet. Its a way for apples to be compared to apples.
Yes, companies may say they side impact test, but there is no standard that they test to...literally they can throw something at the side of the seat, see the shell doesn't crack and call that a side impact test. Its not fair to compare seats that supposedly side impact test to ones that do not because there is no factual comparative basis by which to compare.
As for the anti submarine clip, it can sometimes be a false sense of security. The belt needs to fit a child properly without the clip for the booster to be deemed a proper fit. If the belt is riding up without the clip then either the seat doesn't fit the child correctly or the child is too small for that seat/isn't booster ready. In theory its a great idea, but in reality if the booster doesn't fit, the booster doesn't fit.
Even the best marketed seats have recalls. Britax just recalled a bunch of Chaperone infant seats for an incorrectly installed rivet. The Radian models have had their fair share as well for various issues. There has been much debate over recalls and quantity...something to consider is market share - when a company has 4 times as many seats out there, the numbers of one recall is going to seem astronomical. When you look at the statistics, it doesn't necessarily mean their seat is bad, it just means they average what the other companies with less seats out there average. Price doesn't necessarily dictate recalls. Transport Canada is always working to ensure your child is safe. The defect investigator is not going to let potentially life threatening flaws in a seat go without a recall.
The best seat is always the seat that fits your child correctly, is used correctly each and every time your child rides in it and is installed correctly with the installation being checked to make sure its tight on a regular basis. You are also going to have people strongly encouraging extended rear facing and there are seats that can possibly do this more effectively than simply limiting yourself to 2 brands. If a steel frame is important to your piece of mind, then thats different - thats a preference. But there is no statistical evidence proving its going to keep your child any safer than a seat that doesn't have a steel frame.