Assuming your matte painting is to be used as a texture projected in the Y....
If you know a matching coordinate (Lat/Long) between your matte painting and the GeoTIFF file, you can go to the planet node's [Lat/Long at Apex] fields and enter the GeoTIFF's coordinates. Load in the GeoTIFF file and it will automatically centre at the planet's apex. After that, it's just a question of scaling the texture to fit precisely, making sure that the texture Image node is centred (not Bottom Left). If the MP/texture doesn't precisely match the GeoTIFF input, then calculating any offsets should be straightforward or nudge-able. I've made half of an entire US state using GeoTIFFs of various resolutions and multiple Y-projected textures by doing the above.