Only in the eyes of Canada. There are a few cases about renunciation of US citizenship (Kawakita comes to mind, another is, I think, Lynch), and the US does NOT recognize a US citizenship renunciation performed as part of obtaining citizenship in another country. partly, this is to preserve the ability to try a person for treason. A non-citizen cannot commit treason.
No interestingly the references are about Americans calling the American consulate and being told they were taking an irrevocable step by becoming Canadian citizens. I suspect the draft dodging was part of the issue and a strong stance was mandated by the State Department. I also suspect a “don’t ask don’t tell” mechanism operated. Just come back and never tell anyone official and who would know you had become a Canadian citizen.
I am interested in the neighbor saying Cruz’s mother had applied at the consulate in Calgary after Raphael’s birth and was told the child had no American status because she had renounced her citizenship. Grain of salt operating here and the reference has been scrubbed since yesterday from the internet. The family just coming back and leaving things lie dormant would seem a good way to blend back in.