Finally got some time to breath and can give you all the update on how to pass query parameters from an activity to the application canvas page. The trick is to use the query parameter appParams on the href, and pass on a json-like structure.You can pass multiple values. In the example below I will pass on two parameters 'a' and'b' with the respective values 'a value' and 'b value'

Imaging I define a tempate as

${subject} rated the car <a href='${canvasUrl}&amp;appParams=${params}'>${carModel}</a>

Subject and canvasUrl  are system variables, so when raising the event I only have to define a value for "params"and "carModel":

params[opensocial.Activity.Field.TEMPLATE_PARAMS] = {  

    "carModel": "Toyota",

    "params": "{\"a\":\"a value\", \"b\": \"b value\"}"       

};

This will result on a url target for 'Toyota'

http://profile.myspace.com/Modules/Applications/Pages/Canvas.aspx?appId=120604&appParams={%22a%22:%22a%20value%22,%20%22b%22:%20%22b%20value%22}  

 The values from the query parameter can be retrieved by your javascript code

  var param_value = gadgets.views.getParams().appParams;  

  //or directly  

  var a_value = gadgets.views.getParams().a;

 

If you get these query parameter onLoad, you can directly go to your relevant page section. 

 

Hope this helps. 

 

Marco