I have the same car
On my 300E the oil filter is #102 184 01 01 and is a standard "canister type" of filter located on the top of the engine just behind the air breather. You mentioned the filter being inside a canister, you may be seeing the power steering filter canister. The drain plug is at the left front corner of the oil pan. You will have to lower the plastic skid plate that covers the engine compartment to reach the plug. It does help to have some ramps to get clear access to the oil plug. I have found that removing the filter will spill a fair amount of oil on the back of the engine, so be prepared to clean up the spill. BTW, this topic has had a lot of traffic, so you may want to do a search. Have fun!