Either can support an L-1A petition, and the choice follows the facts rather than preference. Executive capacity turns on directing the management of the organization with wide discretion under only general supervision; managerial capacity turns on managing a department, function or subdivision and supervising professional or supervisory staff.
Pick the capacity the charts can actually carry
Both roles qualify, so nothing is lost by choosing correctly and much is lost by choosing loosely. Delphine's Canadian position, answering to shareholders and setting the plant's direction through a superintendent and two managers, sits naturally in the executive description. Her American position may not, at least at first: a newly acquired plant with a flat structure gives her a department to run rather than an organization to direct.
A petition framed as executive on both sides then has to prove something the American chart cannot show, and a request for evidence follows. Framing the American role as managerial, with a named subordinate layer she supervises and an essential function she controls, is often the stronger and more honest case. Whichever is chosen, the year abroad must have been spent in a qualifying capacity too, and that is proved by the Canadian chart, not by the title.