Does eTA allow me to exit and re-enter Canada?

Question

I'm an exchange student, and I'm staying in Ontario, Canada for a semester (from September to December). I'd like to visit the US by bus and come back, and I'm aware of ESTA (which to me is just the US version of Canada's eTA). I have a couple of questions:

1. (Most important) Would I be able to exit Canada, visit the US by bus, then come back to Canada, given a valid eTA and a valid ESTA?
2. My eTA was approved ~5 minutes after my online application. Is this the case for ESTA as well or am I running the risk of not getting my ESTA in time if I apply now (I'd like to travel in ~3 weeks from now)?

Sidenotes:

• I've seen this question, but I'm not sure if it would be the same in my case.
• I'm a Greek citizen, so AFAIK no special visas are required for me, apart from eTA/ESTA of course.

Answer 1

eTA is not a visa. You can use it to enter Canada as many times as you like while it is valid (unless something substantially changes in your circumstances). Usually it expires after five years or when your passport expires.

Also you do not need an eTA if you are arriving in Canada by land. It is only required if you are flying to Canada. You also do not need an ESTA if you arrive in the US by land.

Neither the US nor Canada require you to have any kind of permit in order to leave.