At the risk of winding up, within a few minutes, as one of those who tried to help, I shall give it a shot. At the very least, I am a Japanese-speaker.
To me, the two sentences mean very different things from each other and they are not interchangeable. That is unless you have a particular situation in mind that is beyond my imagination.
「今週{こんしゅう}の週末{しゅうまつ}でもいい？」
This question is asked when the speaker wants/needs to do something with/for the listener and wants to know if this weekend is convenient for the listener.
「いい」 here means "convenient" or "good" for doing something.
「今週の週末はいい？」
In this sentence, the meaning of 「いい」 will be quite different than in the first sentence. It means "good (without doing something)".
Suppose you bring home-grown vegetables to your friend's home on weekends on a fairly regular basis. This coming weekend, however, your friend is going on a 4-day trip and will not be able to consume the vegetables if you brough them. When you find out about your friend's trip on the phone, you might say 「じゃあ、今週末はいい？」 meaning that it would be good for both you and your friend if you did not bring vegetables this weekend.
This usage of 「いい」 (and of 「は」) is extremely common among us native speakers, but not at all among J-learners as far as I am aware. We speak like:
Mom: 「明日{あした}はお弁当{べんとう}いる？」"Do you need a bento tomorrow?"
Son: 「明日はいい。明後日{あさって}お願{ねが}い。」"No, thanks! I'm fine (without a bento) tomorrow. Please make one the day after tomorrow."
