There's a scene where they show clips of Rider 1, Super 1, Black RX, and Kuuga fighting, as well as aan image of Fuuto tower, heavily implying W as canon for Fourze.
And for OOOs being canon for Fourze, that goes into vague territory, because while W has some sort of version of OOOs being canon, there is no possible time in OOOs for his appearances in W Forever or Movie Core War to be anywhere near canon, as there was no time where eiji ran around with not only the Tatoba combo, but the kamikiri medal as well. Furthermore, Movie Core War contradicts OOOs canon completely.
Honestly, it means that if W is canon, completely, than there IS an Eiji Hino out there as OOOs, but the events of OOOs either haven't happened yet or happened differently. The fact is that there are other version of other riders that exist in other universes, shown to us as being canon as The Begins Night/Decade movie's alternate universe's Skull appearance.
To be honest, its really fucking hard to connect W to OOOs to Fourze due to timeline and canon inconsistencies. W's foundation X shows that it has knowledge of the core and cell medals, but don't exist at all in OOOs it seems.
An Eiji shows up in W forever, but the only time he held onto medals in OOOs was for a brief period and only then he had Tatoba, but an Eiji who has Tatoba and Kamikiri with no Ankh shows up in W Forever. And fuck Movie War Core, as its IMPOSSIBLE to fit in OOOs canon due to massive inconsistencies, making the only other time OOOs and W appear together noncanon as well for OOOs.
As For Let's Go Kamen Rider, it also really can't fit into canon.
Then we go to OOOs to Fourze, which while the ending of OOOs has Kengo and Yuki with a switch, we run into the fact that Fourze heavily implies the events of W are canon in Fourze, which leads us back to the canonical W/OOOs conundrum.
Either way, Rider continuity's pretty fucked up, especially OOOs, whose own movie is not canon, which is pretty fucking sad because it looks pretty cool. But because continuity's so choppy, you could say that OOO's events are canon, you just can't look too close at continuity if you do.