Actually, burning is probably the best way to deal with any excess methane. Methane has a significantly higher warming potential than CO2 does. So if there's any methane we're venting into the atmosphere, we should burn it to convert it into CO2. Bonus points if you can use the generated energy to capture the CO2 as well.
https://archive.epa.gov/climatechange/kids/solutions/technol...
If the landfill can generate electricity that would otherwise be generated, it will convert the CH4 more efficiently than a bus and you don't expand energy upgrading it.
You can power the bus with the already high quality CH4 you extracted from the ground that you would have otherwise burned in to generate the electricity.
I was reading somewhere that in buses in cold climates, heating is actually what eats up all the energy in an electric bus. ICE buses just use the waste heat from a combustion engine.