Yes, you can use variables in the user views, But you can not use them as a dynamic table or field names.
Yet, here is a solution for you:
@{GCKCMatrix}:
Select @[June].[FIRSTCARD] From @[June] where @[June].[GCKC]=|->[Card1Sku] AND @{Month} = N'June'
UNION ALL
Select @[July].[FIRSTCARD] From @[July] where @[July].[GCKC]=|->[Card1Sku] AND @{Month} = N'July'
and a variable "Month", should contain the month that you want.