This quote was written by Henry Kelsey in his journal on August 6, 1691: "this river breants away much to ye Southward & runneth through great part of the Country". Kelsey was born around 1667 in or near London and worked for the Hudson's Bay Company in Western Canada. I haven't been able to find any reference to "breant" online. I no longer (unfortunately) have access to the complete OED. My speculation is that it means "bend."
In the following book Three Hundred Prairie Years: Henry Kelsey's "Inland Country of Good Report" they suggests it might mean “branches” probably based on the following:
on 6 August Kelsey recorded an interesting topographical situation: “... this river breants away much to ye Southward & runneth through great part of the Cuntry & is fed by a lake wch feedeth another River wch runneth down to ye Southward of us.”
This river must be the Etomami, and Kelsey must have been near the present-day town of Hudson Bay, Saskatchewan when he made his journal entry. Once known as the North Etomami, the Etomami gets its name from the fact that it rises in a lake at the “divide,” near which another river rises in a lake in the same valley and flows south. Now known as the Lilian, it joins the Assiniboine near Sturgis, Saskatchewan. In the following days Kelsey recorded his progress up the valley of the Etomami.