Is the default page for hub.mhn.co using a redirect to www.nashman.ca? If so, what is happening is that the forwarding software basically returns a new URI that the browser requests, and the new URI will replace the old one in the browser window and thus in all future requests. You're probably redirecting to ~/hub/ (the hub subdirectory of the site root) which will result in the browser requesting a new URI that keeps the domain name but tacks on the subdirectory.
If you have direct control over the DNS and your webservers, you can use the DNS configuration to direct a request for the hub.mhn.co domain directly to the /hub subdirectory of your webserver. That way, the browser never knows that hub.mhn.co is actually www.nashman.ca/hub/. You might have to direct to an alternate port on the webserver and map that port to the subdirectory, depending on your DNS software (IIRC, most can deal with ipaddress/subdir routes, but some can only handle routing to ipaddress:port).
If your IT department does not have direct control/ownership over your DNS routing, or your exact hosting environment, you are more or less at the mercy of your hosting provider. They may be able to set up their environment to do the same thing, or not; all you can do is ask.
EDIT: Basically you have two options left if you're hosting remotely and can't use their DNS to reroute silently.
First option: clone (copy all files from) the web layer of nashman.ca/hub as hub.mhn.co under a different root space in your hosting environment (try to keep any hooks to service-layer code over at nashman so you don't have to copy the whole vertical slice). If you must also keep the UI under the /hub/ subdirectory, you're repeating code, but you may be able to mitigate this with deploy scripts that will allow you to deploy one local copy of your codebase to various locations. This may also cost more as your hosting environment is now hosting two non-trivial sites.
Second option: host the site and/or resolve the calls on your own hardware. As long as you have a public, static IP address through your ISP, you can provide a DNS server that will be the "authoritative" server for nashman.ca and hub.mhn.co domains. Your ISP or a third party domain name registry can provide a "pass-down" route to get requests from the TLD servers down to you. Then, you can route requests to whatever IP address, port and/or subfolder you like; that can be a remote webhosting provider (as long as they don't mind JUST hosting your site) or your own webservers. This will require the hardware, and a static IP from your ISP. If you lose power to this server, your site will be unreachable until power's restored. If the IP address of your DNS server changes, your site will be unaccessible by DNS until the server that routes requests to you updates its routing table with the new IP (which can be up to 24 hours).