An example using DynamicWrapper
:
f = DynamicModule[{},
DynamicWrapper[Dynamic@Point[{##}],
If[CurrentValue["MouseOver"], col = Red; pt = {##}; ps = 0.04;,
col = Black; ps = 0.02; pt = {};]]] &;
dat = {{1, 2, 3}, {4, 5, 6}};
Graphics[{PointSize[0.02], f @@@ Transpose[dat],
Dynamic@{Opacity[0.5], col, PointSize[ps], Point[pt], Opacity[1],
If[Length[pt] == 2, Text[pt, pt, {-2, -2}]]}}, Frame -> True,
PlotRange -> {{0, 7}, {0, 7}}]

Update
I post this to address OP comment (displaying value of second axis). It could be made a lot cleaner but I leave it in case it can be suitaly adapted for desired outcome.
fticks = {#, 1.5 #} & /@ Range[0, 7];
Graphics[{PointSize[0.02], f @@@ Transpose[dat],
Dynamic@{Opacity[0.5], col, PointSize[ps], Point[pt], Opacity[1],
If[Length[pt] == 2, Text[pt, pt, {-2, -2}]],
If[Length[pt] == 2, {Arrow[{pt, {7, pt[[2]]}}],
Text[1.5 Last@pt, {(7 + pt[[1]])/2, Last@pt}, {0, -1}]}]}},
Frame -> True,
FrameTicks -> {{Automatic,
Dynamic@If [Length[pt] == 2,
fticks~Join~{{Last@pt, 1.5 Last@pt, {0.02, 0.02},
Directive[Red, Thick]}}, fticks]}, {Automatic, None}},
PlotRange -> {{0, 7}, {0, 7}}]

Tooltip
in the documentation? $\endgroup$BubbleChart
! $\endgroup$