I want to replace my 2010 Nissan Versa Engine Computer Module.(ECM)
Although it is around $70 in used, to work it needs to be reprogrammed to the car's VIN number,
otherwise it won't be able to work with car's existing BCM (Body Control Module) (Immobilizer, etc....)
So far I have found Flagship One and ZappAuto only, selling pre-programmed ECM.
Any suggestion about other places ? Perhaps somebody in Canada ?
Thanks!

You're mixing apples and oranges here. The security information from the key and the actual VIN number are stored in different places in the ECM and are programmed separately. When replacing an ECM on a non- I-key vehicle, the sequence is:
1) Program the keys (so the security lamp is out, the ignition will turn on fully, and all systems are awake)
2) Program the VIN
3) Perform Closed Throttle Position Learn (CTPL)
4) Warm up the engine and perform Idle Air Volume Learn (IAVL)
If changing or updating the ECM firmware in addition to replacing the unit, that should be done between steps 1~2. When getting a used ECM, the important thing is that the Hitachi part number on the outside of the unit must match. The Nissan part number depends on the firmware you install, it can be programmed arbitrarily to whatever number is correct by doing a "blank reprogram" using the ROM ID listed in the Nissan parts catalog.

Thanks for the info.
However, as far as I know, the key's code is generated from the VIN, so if the replacement ECM with the same Nissan Number, than it will be wiped clear, added the new VIN and programmed according to car's features.

The code you're referring to is generated by the Nissan database according to the VIN, and unlocks the BCM for storing new key data. The ECM doesn't know that exists and doesn't require having the VIN stored to program keys.

So the BCM and the key communicate with each other and as long as neither changed, they will be working fine, is that correct ?
As for the ECM, the original has MEC901-180 B1 0509B printed on a label. I just need to find one with same part number, right ?
Would BCM & ECM communication work, if now the ECM has different VIN ?
In case, if I can not find one with MEC901-180 B1 0509B, and I would provide my VIN number to Flagship One/ ZappAuto ---can they reprogram a similar ECM with same features ? (1.8 L, AT, CVT, AB)
Thanks!

No, but during programming the ECM gets its new rolling code from the BCM, so it doesn't care about its internal VIN information. It simply stores what the BCM tells it to store. The MEC901-180 B1 is the only part of the Hitachi number that matters, the remaining numbers are date and manufacturing codes. I see tons of them on eBay from $32 up.

What would the car do if I get a MEC901-180 B1 from E-bay and just put it in ?
Thanks!

It won't start until the keys are programmed. It will crank but the ECM will inhibit spark.

key programming needs to be done by a dealer , right ?
Also I am curious about, what will the mileage counter show with new ECM ?
Is the mileage stored in ECM or BCM or somewhere else ?
Thanks!

Most locksmiths can do it on non- I-key Nissans, you don't necessarily need a dealer. Mileage is stored in the cluster, the ECM and BCM have no notion of it. That's different on some of the newest models, but not on yours.