So it wasn't German very long, only 50 years.
As for Montreal, it will be interesting to see how the city evolves. I notice more English in my neighbourhood than when I moved in (8 years ago). But, there is also more French in the old anglo neighbourhoods of the west.
One factor is that a lot of "allophones" are perfectly fluent in both English and French. When you add in the francophone tendency to switch to English when dealing with anyone who shows even a whiff of not being a native francophone, a lot of francophone majority neighbourhoods may see English conversation.
(I'm perfectly fluent and speak French in public. But for the life of me I can't francophone friends to speak French. I think they all want to practice their English. Also, the Quebecois that care about Anglicization probably don't move to urban montreal)
Maybe they don't speak it normally, but I'm pretty sure a lot of people there can speak German. You can literally take a city bus (or walk) over the border into a German town Kiel. And everyone speaks German there. There are people who work in Strasbourg and live in Kiel, or vice versa.
The Alsatian dialect was always more of a rural thing. Both French and the Nazis suppressed it so unfortunately it's pretty rare these days. Still, according to Wikipedia, 43% of adults in Alsace could speak it in 1999. [1]
I used Welsh, Irish, Catalan and French-in-Quebec as examples because they're all languages that declined (to varying degrees) over several centuries under (varying degrees of) government suppression, experienced a partial rebound in interest and popularity in the 20th century after government policy was changed to encourage their use, but ultimately returned to the same trend of declining usage, something like
100|
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0|suppressed encouraged
Where the government intervenes in the opposite direction, the transition can be much more rapid. Visiting Strasbourg (in Alsace, France), people's surnames, street and place names, and the local cuisine are all German, but nobody speaks a word of it. It was amazing (and slightly depressing) to see how in 2-3 generations a city could forget the language it spoke for nigh-on 1,500 years.
The way things are going, I wouldn't be surprised if Dutch were considered a dying language 50 years from now.