>> Trump DOES have standing to sue the Canadian <<
Tell it to the judge, as the saying goes.
And if he does, he could get laughed out of court and even assessed costs for filing a frivolous suit.
Trump has standing because Cruz can damage his chances to get the nomination or any other candidate being damaged. Being damaged by Ted Cruz meets the court Standing Doctrine.
You are not correct. See Davis v. Federal Election Commission
SCOTUS decision and cases cited therein.
Note the following passage from that case: “A party facing
prospective injury has standing to sue where the threatened
injury is real, immediate, and direct. Los Angeles v. Lyons ,
461 U. S. 95, 102 (1983); see also Babbitt v. Farm Workers ,
442 U. S. 289, 298 (1979) (A plaintiff may challenge the
prospective operation of a statute that presents a realistic
and impending threat of direct injury). Davis faced such an
injury from the opera- tion of §319(a) when he filed suit.
Davis had declared his candidacy and his intent to spend
more than $350,000 of personal funds in the general
election campaign whose onset was rapidly approaching.”