I doubt that Clinton is struggling this much with Colorado. She certainly wouldn't be ahead of Cruz by only 3%.
Few voters know who Cruz is. I think he benefits here from being a Republican with a Hispanic last name.
Cruz would most definitely not do that well, he's a poor fit for the state. Quinnipiac isn't always that great with polling, they can be off in either direction from time to time.
The Cruz numbers really don't mean much, because his name recognition is so poor. The Christie vs. Biden and Clinton numbers aren't much out of line with the previous polls. And Quinnipiac did do slightly better than PPP in Nate Silver's 2012 ratings.