This doesn't really go with the spirit of backbone, but I assume since you are talking about Backbone routes you've read the documentation on them.
You can parse out these parameters from window.location.search.
// get rid of ? at the beginning.
var searchstr = window.location.search.slice(1, window.location.search.length);
// split each search parameter into array.
var parts = str.split('&');
var params = {};
// Loop through parts and parse key=value string into params.
for(var i= 0; i < parts.length; i++) {
var pair = parts[i].split('=');
params[pair[0]] = pair[1];
}
that will give you
Object {filters: "1,2", unselectedFilters: "1"}