Another American here. Thanks for bringing attention to this issue among the MTB community in Canada. I support this boycott in concert with other actions against Vista Outdoor, and #NRAboycott as a whole.
It's a tough spot to be in for bike shops, Bell/Giro/Blackburn/Camelbak employees, and sponsored athletes for sure. Taking a guess that many of those that will be affected don't share the positions and politics of Vista Outdoor, and a fair point can be made that boycotting Vista's cycling holdings won't sway their support of the NRA. Bike Portland and Red Kite Prayer have covered this in detail.
A sad reality of the gun regulation debate in the US is that motivation spikes after every tragedy, then fades. So the time is now to send any message we can, keep up the pressure, and hopefully-beyond-hope get action from government. It's the NRA in particular that callously and repeatedly stands in the way of the most basic reforms. For example, since 1996 our Center for Disease Control has been barred by NRA-backed legislation (the Dickey Amendment) from researching gun violence as a public health crisis; we don't even know the full extent of the crisis.