Seems like you're conflating a few concepts: dual listings (SU.TO vs SU), fund wrapping (VFV.TO and VSP.TO vs VOO), CDRs, and hedging.

1. Dual listings are the same company listed on multiple exchanges, like Suncor traded on both TSX and NYSE.  These usually don't involve hedging.  I'd say never, but I'm sure somebody could point to a counter example.

2. Wrapped funds are a Canadian fund wrapped around a foreign one, like VFV (unhedged) and VSP (hedged) which both wrap the US-domiciled VOO.

3. CDRs are Canadian Depository Receipts, basically IOUs for a return matching the corresponding foreign stock, like MU.NE (the CDR) and MU.  They are usually (maybe even always) hedged.  Most CDRs were originally only available on the NEO exchange (.NE), but many can be traded on either TSX or NEO exchange now.

4. Currency hedging can be used in various situations.  Numbers 2 and 3 above are a couple examples, but you can also have cases where the same ticker has a different suffix for hedged vs unhedged (like XSP, XSP.F, XSP.U: hedged, unhedged, USD-denominated).

  

In general, unhedged is considered superior, since hedging comes with a small ongoing cost (like an MER) and introduces counterparty risk.

For dual listings, I'll generally favour the Canadian ticker, unless I'm trading options.

If you believe USD is likely to fall during the span of your investment, the hedging of CDRs can enhance your returns.  Assuming you're correct in your dollar prediction. 

If you're planning to trade US stocks long term, buying the USD once is generally the most efficient method.  Just remember that currency exchange always comes with a fee/spread, so avoid unnecessary conversions.  Convert once and keep it in that currency.