The trend in recent years, is people would go to a location for EWAT (Employment While Awaiting Training?) after BMQ, but they had to go to a location that had a place for them. 2 years ago, I was managing 20+ ppl who had completed BMQ and were waiting for a QL3 course. Until then, they aren't posted and some were separated from family/home. The wait then for a QL3 was 12-18 months. I usually saw this called "pre-positioning".
The word "posted" to me = complete initial training in Winnipeg and being posted to a Squadron. Between BMQ and Winnipeg QL3 isn't necessarily a posting (as in a cost move and can bring family) because you haven't completed the initial training yet and there fore the trade hasn't assigned you to a fleet and Sqn (which indicates where you're going, geographically).
So...a bit of a wait, some uncertainty and no guarantees. However, I was able to get one guy who was married with a wife in Edmonton re-assigned to Edmonton for 408 while he was waiting for his QL3 course, so it is possible...just not a certainty.
If you are close to Comox or Pat Bay you have a better chance of doing OJT/EWAT there...
Re: how long to be qualified (18 months, 3 years...)...that depends on what aircraft you are posted to. The MH course is a bit longer than the LRP one. Maybe by the time you get thru, they'll be posting NWGs (New Wing Grads) to Fixed Wing SAR...and no one knows exactly how long that OTU (operational training unit) course is going to be yet.
So..."depends". I know, not much of an answer but its the accurate one.