Questions about windows

We are in the process of getting submissions to replace our windows, and being in Ottawa (Canada), we are looking for the most energy- efficient windows we can afford.
We've done our research (ain't Internet a great thing?), but we're getting confused by the sometimes contradicting messages from the tradespeople who've come to our house.
Examples:
One contractor suggested that we replace all protuding North-facing windows by same size, flat windows. Better energy efficiency, he said. Two other contractors saw the bow windows and didn't seem to think they were a problem.
Internet searches indicate that Western Red Cedar was a good (albeit expensive) choice for window frames, since it didn't rot. But even the contractors who do sell it seem to try to convince us to go with "good quality vinyl" (PVC) instead.
One contractor told us that aluminum-covered wood (pine) frames came in two qualities: poor and good, the good being made of "extruded aluminum", which meant that there was a space between the wood and the aluminum so that air could circulate.
One contractor recommended INEX spacer bars. Another said that INEX spacer bars were the worst, and recommended SUPERSPACER or INTERCEPT.
Can someone help us make sense of all this?
Also, most websites I've read deal with the windows themselves; they don't talk about their installation which seems to me to be very important as well. What type of installation would be recommended? Sprayed polyurethane? Insulating wool? Both?
Thanks for any help you can provide.
B.
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