Pictures would help folk make suggestions.

Wouldn’t you want an evergreen to provide screening all year long?

I believe some can be pruned of their lower branches to provide a view under the canopy such as in the Jardin des Tuileries in Paris.

Maybe consult a certified arborist in your area for suggestions?

won't spread over property line) that will have significant canopy to cover for privacy = two contradictory objectives. As in either they will have big, screening tops or they won't.

Speaking of big something like an Armstrong maple will grow quite large in time. As in over 60' tall, with a proportionate spread.

As for fast even something like a Freeman maple (such as 'Armstrong') will need decades to reach a certain size - how long are you willing to wait to solve the problem be erecting a tall living screen?

Or is there something else you can do, closer to where you will be looking from? Something that will in fact give quick results?