Not automatically. It depends on whether the Canadian entity still owns or controls the American one afterwards, and whether the new investor's rights amount to control.
Ask where control sits the day after closing
The qualifying relationship is defined by ownership and control, so the test is applied to the structure that will exist, not the one that existed when the plan was made. If an outside investor takes twenty-five percent of the Canadian parent while the founders retain seventy-five percent and the parent continues to own the American subsidiary outright, the chain is intact and the transaction is largely an evidentiary matter. The analysis changes if the investor's shareholders' agreement gives veto rights over major decisions, if shares are issued in a class carrying disproportionate votes, or if the American subsidiary is transferred out of the parent as part of the deal.
Each of those can move control without moving a majority of shares. Have the term sheet read for this before it is signed, because amendments are cheap at that stage and expensive afterwards.