No. Days spent in the United States on the foreign employer's business are not counted toward the year, but they do not break its continuity. A manager employed full-time in Canada across the last three years still satisfies the rule even with regular trips, provided the trips were for the Canadian employer and not US employment.
Trips subtract days but do not restart the clock
Hypothetical example: the irrigation contractor's regional manager has made roughly thirty trips to Washington over three years, none longer than a week, to inspect the subsidiary's installations and attend orchard trade shows on the Canadian parent's account. Each of those days is excluded from the count of foreign employment, but the year of qualifying employment is measured across the full three-year window, and she has been continuously on the parent's payroll throughout.
The case would look different if she had spent nine months seconded to the subsidiary on US payroll under some other status, because that period would neither count nor be neutral; it would need to be explained as US employment and the remaining Canadian time examined on its own. The petition should also confirm the Canadian role was full-time and managerial in substance, since the year abroad must itself be in a managerial, executive or specialized-knowledge capacity.