I don't think they ever went after the C Series. They lobbied the US government to impose a 500 percent tarrif on the C series in order to bankrupt Bombardier and it pretty much worked.
Even Airbus would constantly slag the C Series. They have a guy who works or worked for them named Lahey (if I recall correctly) who made it his mission in life to discourage airlines from buying the C Series. (Though Airbus never tried to have BBD killed by tarrifs.) It was the last time I respected Justin Trudeau actully when, in response to Boeing lobbying the Trump government to tarrif the shit out of BBD, Justin said, OK, then we (the Canadian Gov't) will not be buying any more Boeing products going forward. (Like the F18 Superhornet.)
Unfortunately for BBD, the airlines were scared to purchase the C Series because BBD was viewed as a risk of bankruptcy and BBD was not seen as big and powerful entity like Boeing or Airbus. In the end, BBD sold 51% of the C Series to Airbus for something like 250 million dollars I believe. I was so deflated when I heard that news. But I'm speculating that BBD had no alternative as the C Series just wasn't selling and BBD could not compete with Boeing and Airbus and there was a very real risk of bankruptcy for BBD. Then, just to make matters worse, BBD sold the remaining 49% of the C Series to Airbus for a dollar. Fuck me. So BBD spent BILLIONS designing that plane (a huge portion of which came from the federal government, the Quebec government and the Caisse). By all accounts, the C Series is the state of the art and an abloutely magnificent plane. But that's the story of Canada isn't it. We come up with all sorts of amazing things, but at the end of the day, we are too small of a country to make take it across the finish line.
To say nothing of the Canadian attitude to "eat our young." When someone or something gets too big for their britches, we like burning them down.