In Canada (and flying overseas) a blade 4" or less was ok. BTW, the boxcutters used on 9/11 were 3" blades, so we're paying for security theatre at this point in funding CBSA or the TSA.
At this point? It's always been security theater at the TSA. I've heard countless stories of people forgetting about a handgun in a carry-on and the TSA missed it, and others where baby milk was confiscated.
I don't know anything about the CBSA, but we (the US) should shut down the TSA, increase the liability of airlines for security, and let the airlines and their insurance decide what's enough security. They certainly couldn't do a worse job...