Has a scientific consensus been reached concerning the formation of the Grand Canyon?
I'm studying Earth Science right now, and I found conflicting reporting re: the formation of the Grand Canyon; whether it was formed singularly by the Colorado River over millions of years, or if it was formed by other processes with the river only filling into it relatively recently.

Yes, it was formed by other processes with the river only excavating into it relatively recently.
The Grand Canyon National Park Service describe the events involved in the formation of the Grand Canyon widely. The sequence of events was as follows:

Emplacement of an igneous and metamorphic body.
Sedimentation over the igneous and metamorphic body.
Uptlift of the complex by tectonic forces forming Colorado Plateau.
Excavation of the Plateau by Colorado River.

Read full explanation at Grand Canyon National Park website.