In three and a half weeks, the Alberta referendum will ask residents if they want to hold a formal vote on whether to stay or leave Canada — and most have their minds made up. An Ipsos poll exclusively for Global News conducted online interviews with 1,500 Canadian adults between Sept. 18 and 22, including 600 Alberta residents.Seven in 10 Albertans said they plan to vote for Alberta to remain a province of Canada in the upcoming referendum on Oct. 19 — a statistically insignificant drop of two per cent from similar polling conducted between May 28 to June 1.Among…