Cross currency swaps are a whole different ball game when it comes to structure. they still fuck me up sometimes when i'm thinking about it

The only kind of cross currency swap that actually exists (is traded) is a basis swap which is a float/float swap. This basis moves a decent amount and is driven by funding risk (secured CDOR vs unsecured LIBOR as an example), interest rates and capital flow (for example in 2008 basis in any usd pair went crazy because of the demand for USD).

When this basis swap is traded, it is priced based on one side of the leg, so for example in USDCAD, one person pays usd libor, one person pays cdor +/- the basis. Basis is not traded between every currency, so if you wanted to do a CADEUR swap, for example, you would have to trade eurusd basis, then usdcad basis, instead of just trading eurcad basis, which doesn't exist.

As a lot of people actually want their cross currency swaps to be fixed-fixed (usually because xccy swaps are linked with debt issuance), when someone wants to execute one of these, they're really doing 3 swaps at the same time which makes things more expensive (spreads are wider and traders need like 1-2 bp for execution). As an example for a usdcad fixed-fixed xccy swap, you need to do a cad fixed-floating, a usdcad basis swap, then a usd fixed-floating swap.

Basis swaps are commonly used to take views on interest rates, especially before a central bank rate decision but most cross curreny swaps are for debt purposes. For example a company will issue in a foreign country and swap the proceeds back for financing purposes. Alternatively a company could issue in their home currency and swap to a foreign currency to fund foreign operations or synthetically create a net investment hedge.