The GTA has an abundance of under-used above-ground rights of way.  None of the listed cities, above, would ever waste the assets that lie idle in the GTA.  Unthinkable.
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Toronto has existing, perfectly good, rights-of way from Union to Richmond Hill that would solve at least 80% of the eastern half of the DRL problem and interchange with the Eglinton Crosstown - without any tunnelling.  With political will, it could easily commence at least partial operation in less than three years.  The stations could be fancied-up later.
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But no, we can't do anything quickly or economically. 
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No.  We blow the whole wad on a useless political boondoggle in Scarborough, or on spending 15 years boring an eye-wateringly expensive tunnel to Pape - that isn't even needed, or that could be built later, anyhow.
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It only took six years to defeat Nazi Germany.
But it takes 15 years to build a tunnel to Pape?
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This is the squandered opportunity of the last five years.
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No compromises ???
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A tragedy.