Oh I didn't think you were arguing it as not canon; I was just trying to rationalize, with myself even, what the relationship actually entailed. I admit the OP thing was overblown with what attention they got in the series, but it was probably to show Suzaku's ideals contrasted with Lelouch's.

Cecile and Lloyd were with Suzaku when Euphie died. They were standing right behind him for a portion of time and could very well have walked out. I actually checked this because I wasn't sure myself. I don't think we could see Suzaku's face well enough in the doujinshi to be sure whether or not he was crying, but as it was a nod to the original story, I'm assuming we are supposed to view it as the same. Since it is heavily focused on LuluEuphie, I think the artist is asking for a benefit of a doubt when it comes to Euphie hallucinating or maybe she's just simply recalling. I think it would be fair to insert both Suzaku's complete and utter emotional breakdown and Euphie's nostalgia into the same canonical timeline if need be. I definitely believe the person with Euphie is supposed to be Suzaku; the artist just didn't go all out with the knight uniform. Hence, why she has the panel of Zero!Lelouch on the page next to it, a reference to his later sad talk of sadness with C.C.