Actually, none of the three is usable as-is, but any of them could be made usable, with a bit of work. Starting with your sentence #1:
- ...there is same probabiliy in selection...
This has two problems: first, you need the definite article "the" before "same":
...the same probability..
Second, it's not clear what "same" refers to. "same probability in selection..." Same as what? Something mentioned previously? No, each node's probability is the same as each other node. But you can't just say "each other" because the sentence does not mention the "nodes" from which the destination node is to be selected! So you need to mention them.
- ...there is the same probability for each node in selection of the destination node.
Still not elegant. It doesn't make clear that one of the nodes must be selected to be the destination node.
Let's move on to #2:
- ..there is equal probability to select the destination node.
In this one you need an indefinite article: "an equal probability".
Also, the phrasing "probability to select" is not idiomatic. You can say "equally likely to..." but not "{same/equal} probability to..." You need to say "probability of [something]. The [something] must be nounal, so use the gerund form "selecting".
Like so:
- ..there is an equal probability of selecting the destination node.
Somehow, this doesn't seem accurate. If a destination node is sure to be selected, there is a 100% probability of "selecting the destination node. We really mean there's an equal probability for any node, but (as in #1) you didn't mention the "nodes"!
You could mention the nodes like this:
- ..there is an equal probability of selecting any of the nodes as the destination node.
Oops... This is still active voice, and we failed to say who/what does the selecting. When you say "to select", this is active voice —you have to specify what (subject) is selecting what (object). And you didn't, and I infer you didn't want to mention, in this sentence, \who or what does the selecting_. Maybe it is clear in context, but you did not give surrounding context. So to get around mentioning who/what does the selecting, try passive voice (with the necessary inversion),
thus:
- ..there is an equal probability of any of the nodes being selected as the destination node.
Better than #1.
Let's see what we can do with #3.
- ...they (the nodes) have the same probability to be selected.
As above, change "to be selected" to "of being selected"
- ...they (the nodes) have the same probability of being selected..."
But the same probabilty as what? You know it's the same probability as each other, but it's awkward/wordy to say "same probability as each other."
It would be clearer and more concise to say:
- ...each node has the same probability of being selected..."
But this still doesn't say what the node will be selected for, because this sentence fails to mention the "destination node"! So we need to mention it, like so:
- ...each node has the same probability of being selected as the destination node
Oops! now it's still ambiguous because there's a misleading "same.....as" structure, implying that the destination node is a separate node that has the "same" probability as the other nodes of being selected (for what, we know not!)
So, take out the "as", and we have:
- ...each node has the same probability of being selected the destination node.
Personally, I like this last one best.