Cruz was born in Canada, and raised in the US. Mother was US citizen, father was Cuban. The parents never applied for citizenship in Canada.
His mother was American, so he is American. Best he could be is dual citizen, as his parents were not Canadian themselves, nor did they seek to be. Plenty of kids are born in Canada to American parents that are working here, and they are considered American citizens.
I agree with you, I think Cruz is probably, legally, Canadian. I wish I didn't think that, though.