Politics is always interesting, but we have a phrase "clutching at straws" which seems to be appropriate at this time.
A single by-election will not change a governments policy. It is quite common for a "protest vote" to be registered during by-elections, but in the case of Labrador, this is not even a protest. Labrador is traditionally Liberal anyway, so is just returning to "normal".
It should not be seen as a change of the general atmosphere in Canadian politics. The Canadian citizens have voted, within the election laws of the land, for the current government and their policy on immigration. They will have the opportunity at the next full election to vote differently if they no longer agree with what Kenney has done. Until then, there is unlikely to be any significant change. In fact, it will probably get more restrictive on immigration, as this appears to be what most Canadians citizens seem to support.