Former Boeing software engineer, worked on engineering simulators (where real hardware was in the loop):
There is an idea of triple channel autolanding, wherein the plane uses the consensus of the three autolanding systems. Should no consensus be available, then the pilot is advised that autolanding is not available.
Other than that, any sourcing from different manufacturers is happenstance. 737 avionics are sourced from a different vendor than 747/757/767/777. And different functions can come from different vendors, although vendor consolidation has cut down on that.
I'm not across what happened post 777, as I left Boeing in 1999.
