Depends on one’s definition of “significant” difference in size (or more accurately, average size).
This article or research paper from 2012 which another member linked to in a different thread, does note differences in sizes of wolves based on region and diet, and noted there was still controversy over this kind of thing.
Abstract. The available scientific literature was reviewed to assess the taxonomic standing of North American wolves, including subspecies of the gray wolf, Canis lupus. The recent scientific proposal that the eastern wolf, C. l. lycaon, is not a subspecies of gray wolf, but a full species...
meridian.allenpress.com
Excerpts:
Development of even more powerful genetic markers has led to new, highly controversial interpretations, * * * * Other controversies include whether the current Great Lakes wolf population is evolutionarily representative of the historical population (
Leonard and Wayne 2008) * * * and the taxonomic identity of wolves of Pacific coastal regions (
Muñoz-Fuentes et al. 2009). The lack of consensus among researchers on so many important issues related to the taxonomy of North American wolves prompted the present review.
Differences in habitat have been correlated with variations in behavior, including migration and prey selection. For example, Kolenosky and Stanfield (1975) have described variation in Ontario wolves, where larger wolves of boreal forests specialize on moose Alces americanus and caribou Rangifer tarandus as prey, while smaller wolves in deciduous forest habitats specialize on white-tailed deer Odocoileus virginianus.
Trends of increasing size among wolves to the north and west of southern Ontario and Quebec have been noted in morphometric studies covering the Great Lakes region. The association of smaller wolves with white-tailed deer in deciduous forests and larger wolves with larger prey, such as moose and caribou, in boreal forests has been frequently cited (
Kolenosky and Standfield 1975;
Skeel and Carbyn 1977;
Schmitz and Kolenosky 1985). When wolf skulls were divided by source habitat into deciduous forest (eastern wolf) and boreal forest (
C. lupus), discriminant function analysis distinguished 75% of boreal wolves from eastern wolves, and boreal wolves were >25% larger in body mass (
Kolenosky and Standfield 1975).
….
This review was initiated because of the wide range of views expressed by different researchers and research groups on some major features of relationships and classification of North American wolves.
cowboystatedaily.com
