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Euschistus sp
It could be the same as the one Dan found in Ontario, Euschistus servus: http://www.projectnoah.org/spottings/750...
But I think Euschistus Ictericus could be worth checking out as well. I have found information that both of them have been found in the Québec area.
There might be more similar shield bugs in your are that I am not aware of, but perhaps this can help someone who has a bit more experience than me.
Best regards