Entirely untrue. FedEx, Con-way/XPO and YRC (for YRCF through Reimer Express Lines Ltd.) all own their Canadian carriers, and that's just in LTL. Schneider National has an in-house Canadian operation, Celadon did until they renamed it Hyndman (after a carrier they purchased that had higher success hiring due to better pay...the pay didn't make the transition) and a few Canadian carriers have even built into the US (Day & Ross USA, TransX USA & Verspeeten Cartage USA/Cordell Transportation come to mind). And prior to TNT selling off TNT Freightways (later USFreightways) their operation was one as well, with Overland Express in Canada taking care of Red Star, Holland, Dugan and Reddaway in the US.
The reason partnerships are more common is because establishing a visible presence in Canada isn't easy. In most cases, US carriers buy their partner. This won't happen with OD though because two carriers service them, and Speedy Transport has a much bigger contract with YRCW to be the Canadian presence of Holland and New Penn. That being said, OD has sent Speedy a van to do P&D with because they want the customer to see their name.
Having that visible presence among their customers, combined with already doing the border crossing part on their own, suggests that OD does eventually plan to establish their own fleet here. I would welcome it.