At first it is need to be considered what is the reason of the two type of river formed next to each other and joining. There have to encounter different tectonic regime or base rock etc, which can promote that situation. For example encountering of slopes of a mountain range with pediments and a gently sloping lowland with different slope direction.

I agree with the above, I cannot note a specific geographical location that this happens in but I can tell you that one place you may see it is in high sloping areas (such as mountainous regions) that lie directly next to a low, flat plain. The meandering stream is usually due to a large amount of sediment in the stream. The sediment that usually makes a stream meander normally erodes from mountainous regions. So if you could think of any places that may be rich in sediment and lie right next to a mountain range that would be your best bet. I'd think of the area just to the east of the Andes that flows in to the Amazon. These are some of the most sediment rich rivers in the world and present a great example of meandering streams, the hard part is finding a straight channel that flows in to them. Perhaps look at the eastern base of the Andes... Best of luck!

lots of examples of this in the Hudson Bay - James Bay lowlands, and south-central Alaska, at least.

I'm not aware of any place as such but it is possible only to those places where a mountain region is juxtaposed to plain. I hope John Youngson's places should be considered. !