The secondment agreement may allocate immigration costs between the Canadian and U.S. entities, or may be silent. Ask in writing which entity covers legal review, document gathering, and filing costs, and confirm current government fees from official sources rather than relying on figures quoted internally.
Put the cost allocation in the agreement
A structure with two entities makes it easy for each to assume the other is paying. Before work begins on the file, get the allocation written into the secondment agreement or a side letter, and ask whether any reimbursement is conditional, for instance on completing a minimum period of the assignment. Budget review time for the contract chain itself, since counsel needs to read each agreement rather than a single offer letter.
Two employers on one file often means two sets of counsel are retained independently, and duplicated review of the same filing adds cost without adding value. Settle early which entity's counsel leads and which only reviews, rather than paying two firms to draft the same petition. Ask whether the fee arrangement is a flat rate for the filing or hourly review of an evolving record, since an assignment with several rounds of contract revisions can turn a modest hourly estimate into a larger bill.
The entity that will actually direct the work in the United States, not simply the one issuing the paycheque, is the one whose records the file needs to document, so confirm early which side is gathering that evidence. Clarify whether reimbursement, if offered, is treated as taxable income before accepting a number without asking how it will be reported.