1.Will it effect the canon much as I love the detail Bethesda put into their games and hope Zenimax Online don't ruin it.
2.Plus will it effect future development of Elder Scrolls? For example this town in Argonia or Elswyere must be like this as it's like that in Elder Scrolls Online? Could effect the detail again and uniqueness.
3.Is this Todd Howard's decision or was he "forced" by Zenimax to do it for greed and money?

1. Not really. They have to follow established canon, which will not do much to affect any of the games that come after it.
2. Can't be certain yet, but after centuries anything could happen.
3. I think it was a joint decision to cater to the fans' desires. That's a good thing, isn't it?

i would think bethesda would be helping with the lore so most stuff in the game should be according to how lore describes it. i doubt they would choose to make an elder scrolls mmo and not use lore from the series

The Elder Scrolls Online takes place roughly 1,000 years before the events of Skyrim.