Trying if/elseif irule...

Try this and see if it works out for you:

when HTTP_REQUEST {
switch -glob [string tolower [HTTP::host]] {
"myoriginal.ca" -
"www.myoriginals.ca" { 
if { [HTTP::uri] equals "/" } { HTTP::respond 301 Location "https://mystore.net/ca/catalog/index.aspx" }
}
"myoriginals.ca" -
"www.myoriginals.ca" {
if { [HTTP::uri] equals "/" } { HTTP::respond 301 Location "https://mystore.net[HTTP::uri]" }
}
}
}

Made the HTTP::redirect into a HTTP::respond because an HTTP::redirect is a 302 (Temporary). With HTTP::respond you can specify the HTTP::status to a 301 (Permanent)

The "myoriginal.ca" - tells it to follow the same action as the one below it (you can keep on doing this if you have more that you want to follow the same action.