I haven't tried it, but you probably can listen to Routes_Registered event to register Catalog route. That way the Catalog route will be registered last and be overridden by the cms route. Might not work, but it is easy to at least try.

Thanks for the response Quan.

To be honest I'm not sure where to register these events listeners and exactly how I register the catalog routes. 

    [InitializableModule]
    [ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
    public class RegisterCustomContentRouteInitialization : IInitializableModule
    {
        public void Initialize(InitializationEngine context)
        {
            EPiServer.Global.RoutesRegistered += RoutesRegistered;
        }

        private void RoutesRegistered(object sender, EPiServer.Web.Routing.RouteRegistrationEventArgs e)
        {
          // Do something here, but what, exactly?
        }
    }

Is this what you mean when you say listen to the Routes_Registered event? And would I check the sender object or e argument and then register a route?

You can look for CatalogRouterHelper usage in your code which should be registering the route, then move it here

Thank you, Quan!

I managed to register the catalog routes after the CMS content routes were registered but it didn't produce the desired result. I'm all ears if you have any other alternatives that may solve this.

I would suggest to try this out https://github.com/episerver/DeveloperTools  so you can see the order of routes registered. if they are as expected (i.e. the catalog route is registered last) then ... we need to think of something else 

When I debug during startup I hit the breakpoint for registering the CMS routes before the Commerce routes but in the developer tools they still end up under the Commerce routes. Is this order saved to a database perhaps, would I need to clear it before running the route registration again?

No the routes are registered in memory and not saved in DB. That is very strange ... 

In my experience the CMS pages has the higher priority in these routing cases... if you unpublish/expire the commerce node do you end up on the cms page then?

Thank you for the suggestion Erik. If I expire commerce node I get a 404. However other pages that does not match a commerce node renders correctly.

This is my CMS page structure

/new-york
--- /pizza -> Also matches a commerce node. Gives 404 when the commerce node is expired / unpublished. Prioritizes commerce node if it is active.
--- /burgers -> Does not match commerce node. Renders cms page correctly.

All right, so I finally found a solution. Based on Quans suggestion to register the commerce routes last I instead wait for all routes to be registered and manually switch out the "pages" route handler to a lower order/index in the RouteCollection list (giving it higher priority). This seems to produce the desired result. Are there any drawbacks of this that we should be aware of? As you might have noticed I'm not completely on top of Episerver internals.

  public class SiteInitialization : IConfigurableModule
    {  
        public void Initialize(InitializationEngine context)
        {
            // Setup code...

            EPiServer.Global.RoutesRegistered += OnRoutesRegistered;
        }

        private void OnRoutesRegistered(object sender, RouteRegistrationEventArgs e)
        {
         
            // This method will wait until all routes are registered in-memory by Episerver
            // Then it will find the route handler for regular EpiServer CMS pages move it to a lower order than the commerce pages, giving it higher priority
            // if a cms and a commerce page exists at the same url.
            var defaultRoute = e.Routes
                .Select(r => r as DefaultContentRoute)
                .Where(x => x != null)
                .First(x => x.Name.Equals("pages", StringComparison.InvariantCultureIgnoreCase));

            var indexOfPagesRoute = e.Routes.IndexOf(defaultRoute);

            e.Routes.RemoveAt(indexOfPagesRoute);
            e.Routes.Insert(10, defaultRoute);
        }
}