Filling the black wings in a portrait clip on a landscape canvas

Hi -Thanks for any help

i  am making a little movie in Rush and I have portrait clips that I have to fit on a landscape canvas. I don't really want zoom in. Is there a way to get that effect where a blurred, enlarged section is used to fill the back ground - like a filter or something? Or is it just a question of adding another layer underneath and bluring / zooming in on it?