Rumours about Amazon Video coming to Canada have been around for several months. I suspect the execs at shomi knew that Amazon was coming to Canada, since reports are that Amazon has been withholding international rights to the more recent programs that they are producing themselves and are also acquiring rights from the Hollywood studios.
The Rogers board came to the conclusion that shomi could never turn a profit while competing against Netflix, Amazon and CraveTV. I think the exact timing is a bit of a coincidence, but I believe the fact that Amazon Video was coming to Canada forced Rogers to evaluate their prospects for the service. Shaw had already written off their entire investment and probably were no longer interested in being a partner since they had sold all their media assets to Corus (which didn't want shomi.)