CN Tower; Unlocked at Mass Media, +5
in this City... +10%
Global Output... +2
GE... must be built in a city which has a Lake nearby & a Stadium.
Channel Tunnel; Unlocked at Stealth, Lowers cost of Road+Railroads maintenance by 75%... +10
... +3
GM... must be built in a coastal city that has both an Harbor and a Seaport.
in this City... +10%
Global Output... +2
GE... must be built in a city which has a Lake nearby & a Stadium.Channel Tunnel; Unlocked at Stealth, Lowers cost of Road+Railroads maintenance by 75%... +10
... +3
GM... must be built in a coastal city that has both an Harbor and a Seaport.
income, +4
, requires plains.
base 
bonus as listed in the OP. That would be massively overpowered. I think instead it could be like a super-improvement, allowing movement of ships over, maybe, two land tiles from one ocean to another, with a
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