No. Paying the processing fee confers no status. Until permanent residence is granted under the carrying category he remains subject to ordinary rules on entry and activity, and managing a U.S. business full time on visitor status is not permitted. Sequence the move after the grant, not after the payment.
The fee starts a process; it does not change what he may do tomorrow
The published sequence is application and processing fee, vetting, gift and then immigrant processing under EB-1 or EB-2, with the applicant becoming a permanent resident only when that final step is complete and a visa number is available. At no earlier point does he hold any U.S. status by virtue of the program.
A Canadian citizen may enter as a visitor to attend to certain business matters, but running a farming operation day to day is employment, not visiting, and doing so while awaiting a Gold Card decision risks a finding of unauthorized work that would affect the very application he is waiting on. If he needs to be present and active on the land before residence is granted, that need has to be met by a category that permits it — for example E-2 if the farm is a real, non-marginal operating enterprise he owns and directs, which is a separate application with its own conditions. Plan the relocation, the sale of Canadian assets and any change in how the U.S.
land is farmed around the grant of residence, and re-verify the program's terms before each payment.