The construction of the Philipsburg interchange is slated for an undated phase IV, along with the Saint-Alexandre interchange. Although a design for thie Philipsburg interchange has been made public, there has been no land acquisition, thus probably no definitive planning. There is hardly 1,000, nay 2,000 vpd on this section; nothing justifies grading quickly the scarce intersections with low-volume roads or dead-end streets south of Pike River.
Just looking at the MTQ website, on the A-35 Project page, Phase IV is still undated, and still reported as "on planning" in the PQI (Plan québécois des infrastructures, or Quebec's Infrastructural Plan), but is on the list of bill 66, accelerating some government projects, adopted in 2020, so it will probably begin in 2023 or 2024, in order to upgrade the last part of the actual QC-133 (the divided part) to interstate standards.
Hold your horses, construction will not begin in 2023. There, you have it : it's listed as
in planning in the PQI, which lists the priorities in terms of infrastructures for the next 10 years. The status remains the same since Saint-Sébastien―Philipsburg and Philipsburg-Border sections were split in two phases in 2019. Funding for the construction has
not even been secured by the Treasury board, so the works are not about to begin since no provision for a contract was made, no contractor was chosen, no tender was received and no calls for tenders was launched ― and I'm not even talking about the needed ministerial authorizations and redtaping.
Regarding the wide range of autoroute extensions that are of debatable relevance, and the funding problem, whether it's the FORT (fund for the maintenance of the road network, supplied with declining income from gasoline taxes) or the rise of interest rates, choices will have to be made, are being made or have already been made. I do not think A-35 phase IV is one of them, for reasons previously mentionned. And when this leg of highway will be built, it will comply not to interstate standards, but to the
MTQ design manuals. The latter differs greatly from the FHWA prescriptions.