Is it canon that Leliana is in love with the warden?

No. She referred to my Warden as a trusted friend and I didn't detect any wistfulness in her voice. That can certainly be part of your headcanon, but I don't believe it is reflected in the game itself.

Also, Cullen's line doesn't necessarily have to refer to anything romantic. It could just be that, due to her experiences with the Blight, Leliana has great admiration and respect for the Grey Wardens in general. That's why she sends you out to find Blackwall, because she has those positive feelings about Wardens and thinks he could be helpful in the current situation, not because she heard what a big bear he is and wants to jump his bones.

having romanced leliana in my first playthrough (since how can i not? ) and i can say as a fact, there is a noticeable difference in the dialogue with leliana between a romanced warden and non romanced warden. also if you destory the urn of sacred ashes she is even bitter toward the warden

As others have said, Leliana feels a connection to the Wardens because of her experiences in the 5th Blight. She also does not have any fond memories of Morrigan. Apart from their potential rivalry for a male Warden's affections, I presume this is because either she abandoned the squad (having been rejected for the Dark Ritual) or slept with the Warden (if male) or was using dubious ancient magical rituals (if the Warden is female).

Anyway, I don't think there is any suggestion that romancing the Warden is canon, although I have to admit that a Warden in a romance with Leliana does seem to get a better ending than anyone apart from a Warden who romanced Morrigan, did the Dark Ritual and when through the eluvian with her.

At least she understands that people other than Bioware decides what 'death' actually means.  :mad:

Leliana is like the clouds,good for headcanons.

No they didn't.  Sixth sense was well written.  The Lellianna retcon was bad writing all the way down.  DG should be ashamed of what he wrote regarding that back then.

I love how everyone talks about Leliana being revived yet always completely ignores Anders and Justice being retconned into always being recruited regardless of your actual choices.

way to miss the joke dear

I was referring to his commentary online that Bioware and only bioware determined what was dead or not regardless of what you thought you did as a player.  IMHO he showed utter arrogance and blatent disrespect for his audience and IMHO that is a sin Bioware has suffered from in recent years.

That's a lame excuse for how they handled Lelianna, and I think we both know it.  If you don't want Lel to die, then don't permit that to happen in Origins.  If you do give the player the choice, that choice needs to be respected.  Doing otherwise shows blatent disregard and disrespect to your core audience.

The choice wasn't to kill Leliana, though.  The choice was to taint the ashes with dragon blood  Which you can do.  Leliana attacking you is a consequence of that choice.  

It's not a conscious choice without metagame knowledge.