Upvote:8
DATV means Direct Airside Transit Visa. The only thing it is good for is being allowed to board a flight towards an UK airport when you do not expect to need to pass immigration there.
If your friends are not traveling themselves, they can't come airside to meet you, so your only chance of meeting up is if you pass through immigration to meet them landside. Having a DATV is irrelevant for that.
You have two options:
There's no reason why you would need to see your baggage during the layover, if you can get the departing airport to tag it through to Canada (which they usually will if your flights are all on one ticket).