1. For transient PAX, to US or other INTL destinations, there is a pro-forma immigration check. To the USA there will be a US TSA style security check, and then US border clearance. I'm not sure if there is another security control to get back on an INTL outboudn.

2. Yes. Leaving a INTL inbound there is only a hallway to a customs/security checkpoint. No services. It is obviously not designed for mingling around.

3. No. But if can "enter" (as opposed to "transit") Canada, then you could hang out landside, I suppose. For you going to the US, this would not be any additional security/customs, since you have to clear anyway, but for them, it might mean one more security process. If allowed.