Wrong.
Mosul has been a multi ethnic and multi religious city since ancient times..well before to the rise of Mohammed. This tradition has continued right up to the withdrawal of US troops from Iraq.
Christians were in Mosul since the 1st century...a Patriarch was named there in the 1500s, a Dominican order was started there in eighteenth century.
Almost ten thousand Jews were recorded as living in Mosul by the Exilarch in the twelfth century.
If Mosul is considered a Sunni city today then it is only due to a shameful failure of Western foreign policy over the past two decades.
Mosul is THE sunni stronghold in IRAQ.