As near as I can tell, I largely agree with Tedronai: evocation maneuvers don't involve a defense roll as such. They *do* require a number of shifts of power that scales to the resisting skill (and therefore implies a control roll needing to be at least that high, with backlash allowing success and fallout causing failure). So my read is that for evocation maneuvers, the target is in effect treated as resisting with their base skill (+0 on the dice).
I don't think it would be unreasonable to allow a roll to resist, though I'd certainly allow the caster to dedicate more shifts of power to the maneuver (ie, a number of shifts greater than the target's resistance) to make the defense more difficult.
As to trying to counter the evocation maneuver once in play, I agree the rules are ... light on the subject. My take (based on the rules, but not spelled out in the rules) is that it should be handled in much the same way that countering a mundane maneuver is, but with the spell effect resisting the attempt. So if the caster did the maneuver at the baseline strength of 3, then that is what the victim would need to roll to undo the maneuver. This also leaves open the option for the spellcaster to overpower the maneuver, therefore making it harder for the target to remove the effect before it expires.
