So what would happen is that all of the improvements along the I-5/205 corridor would be funded by these tolls, freeing up revenue currently spent on the corridor to be used for transit. In essence the tolls would then end up paying for transit, but indirectly
Such would violate the Oregon Constitution. The monies freed up would go right back in ODOT's account, to be used for however ODOT sees fit.
Metro doesn't receive state gas tax funding; it merely has a say in how money is spent within its jurisdiction. Tolling freeways in Portland is just a sure-fire way for ODOT to spend the money outside of the Metro, since there is no requirement other than that gas tax money has to be spent on highways - and not light rail.