While I'm not Canadian myself, but having been on this forum for a quite while, I have observed and researched that there is no specific length limit placed on knives in the law itself. Indeed most beliefs that there is a length limit, even with US state laws, are myths, since only a few states have them.
However, Canadian law permits a police officer examining your knife to use discretion. The legality is based on the intended purpose of the knife, and that intended purpose is assessed based on the circumstances you are encountering the police, your stated purpose for carrying it, the size of the knife, and the design of the knife. It is prohibited to ever carry a knife with intent to use it as a weapon, even if that intent is only for self-defense. While using a knife in self-defense can be legal (if it was justifiable), actually carrying one as a precaution is not.
The Border Guard 5 would be considered a LARGE folding knife, considering the statistical average size of a folder is about 3-4 inches, but it's not huge. I'm not sure how Canadian cops are about color, but the fact that it's all black and has a false edge on top might give the impression it was meant as a weapon. However, the strap-cutter part at the back and the glass-breaker pommel might be persuasive that it's used as a rescue device. It's probably going to come down to why you have cops search you in the first place, which 99% is because you did something else to piss them off.