Occasionally, I make veneer from pieces of resawn stock. I leave the veneer panel larger than necessary when applying it to its substrate. Then, a quick pass with a trim router brings the veneer edges into perfect alignment.
With thin veneer, you can use a climb cut when necessary and not be concerned with the router grabbing erratically. It’s a good way to keep the veneer from chipping or tearing out at the corners. A solid-carbide laminate trimming bit or a flush-trimmer with a sheer cutting angle are both good choices for this application.